]>
ACME Token Identifier and Challenges
iconectivmary.ietf.barnes@gmail.comSTIRToken challengeACMEThis document specifies an identifier and challenge type required to enable
the Automated Certificate Management Environment (ACME) to issue
certificates using a token for the challenge response. This token is issued by a administrative authority with
whom the Certification Authority (CA) has a trust relationship. The entity requesting a certificate also has
a relationship with the administrative authority, such that the administrative authority assigns a unique
code to the entity. This entity code
is included as part of the token that the administrative authority issues. is a mechanism for automating certificate
management on the Internet. It enables administrative entities to
prove effective control over resources like domain names, and
automates the process of generating and issuing certificates. This document specifies an identifier and challenge type to enable
the Automated Certificate Management Environment (ACME) to issue
certificates using a token for the challenge response.
This token is issued by a administrative authority with
whom the Certification Authority (CA) has a trust relationship.
The entity requesting a certificate also has
a relationship with the administrative authority, such that the administrative authority
assigns a unique code
to the entity. This entity code
is included as part of the token that the administrative authority issues. The following diagram summarizes these trust relationships and protocols: | Entity |
| (code) |
| |
+-------------+
]]> There are several use cases that can leverage a mechanism using a generic token
for the challenge response, in particular for Secure Telephony Identity Revisited
(STIR).
The STIR problem statement identifies the need for Internet
credentials that can attest authority for the originator of VoIP calls in order
to detect impersonation, which is currently an enabler for common
attacks associated with illegal robocalling, voicemail hacking, and
swatting. These credentials are used to sign PASSporTs
, which can be carried in using protocols
such as SIP .
Currently, the only defined credentials for this purpose are the
certificates specified in . describes certificate extensions
suitable for associating telephone numbers and service provider codes
with certificates. specifies
the use of ACME extensions to enable certification authorities to issue
certificates based on telephone numbers.
specifies the use of ACME
extensions to
enable certification authorities to issue certificates based on
service provider codes. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in . The intent of the challenges in this document is to provide evidence that an established administrative
authority
has authorized the entity requesting the issuance of certificates. The model is based on the entity that is requesting
certificates being assigned a unique entity code by the administrative authority. The expectation is that the Entity code would
be stable and not change frequently, if at all. The entity also requests the
token that is to be used in the challenge response from the administrative authority, prior to requesting issuance of
a certificate. Entities that are using this mechanism SHOULD define the lifecycle management for the entity code token - e.g.,
the frequency at which it should be renewed. This is expected to vary depending upon the use case. In order to issue certificates based on entity code values, a new
ACME identifier type is required for use in ACME authorization objects. The baseline ACME specification defines
one type of identifier, for a fully-qualified domain name
("dns"). This document defines a new ACME identifier type for entity codes ("EntityCode").
The new "EntityCode" identifier introduces a slightly different authorization process.
A mechanism is required to allow the entity requesting certificates to prove it has the authority to request certificates.
This document defines a new ACME challenge type of "ec-token-01" to support entity code tokens.
The following is the response that the ACME client receives when it sends a GET for the challenges in the case of a "EntityCode"
identifer: ;rel="directory"
{
"status": "pending",
"identifier": {
"type": "EntityCode",
"value": ["1234-0111"]
},
"challenges": [
{
"type": "ec-token-01",
"url": "https://example-ca.com/authz/asdf/0"
"token": "DGyRejmCefe7v4NfDGDKfA" }
],
}
]]> A client responds to this challenge by providing an entity code token.
The entity code token is a standard JWT token
using a JWS defined signature string . The entity code token JWT Protected Header MUST include the following: Defines the algorithm used in the signature of the token. Set to standard "JWT" value. Defines the URL of the certificate of the administrative authority validating the Service Code. The authorization code token JWT Payload MUST include the following: Entity Code value being validated in the form of an ASCII string. DateTime value of the time and date the token was issued. DateTime value of the starting time and date that the token is valid. DateTime value of the ending time and date that the token expires.: Fingerprint of the ACME credentials the requestor
used to create an account with the CA. The fingerprint is of the form: base64url(JWK_Thumbprint(accountKey)). The "JWK_Thumbprint" step indicates the computation specified in
, using the SHA-256 digest . As noted in JWA
any prepended zero octets in the JWK object MUST be
stripped before doing the computation. To respond to an entity code token challenge, the ACME client constructs an entity code
authorization ("ec-authz") using
the "token" value provided in the challenge and the service provider code token ("ecAuthzToken")
that has been previously obtained from the administrative authority.
These two values are concatenated and separated by a "." character as
follows: ecAuthorization = token || '.' || ecAuthzToken The token for a challenge is a string comprised entirely of characters in the URL-
safe base64 alphabet. The "||" operator indicates concatenation of
strings. An example of the use of the "ec-token-01" in a challenge response sent by the ACME client is provided below: Upon receiving a response to the challenge, the ACME server determines the validity of the response.
The ACME server MUST verify that the "token" in the response matches the "token"
in the original challenge.
To determine if the "ecAuthzToken" is valid,
the server MUST use the URL in the JWT header in the "ecAuthzToken" to obtain the certificate associated with the JWT payload.
The server MUST validate the signature and verify the claims.
The "sub" field MUST be the value that was included in the "EntityCode" in the original challenge.
The server MUST verify that the "fingerprint" field matches the ACME credentials for the ACME client that created the
account with the CA. If the validation is successful, the "status" in the challenge object is set to "valid".
If any step of the validation process fails, the "status" in the challenge object MUST be set to "invalid".
[Editor's Note: Likely we should describe specific error responses for the above.]
This document defines a new ACME Identifier type and ACME Challenge type to be registered. [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned to this document ]] This document defines the "EntityCode" ACME Challenge type in the ACME Identifier Type registry as follows:
This document defines the "ec-token-01" ACME Challenge type in the ACME Challenge Types registry as follows:
This document relies on the security considerations established for the ACME protocol per .
The new "EntityCode" identifier and "ec-token-01" validation challenges introduce a slightly different authorization process.
However, the challenges still have a binding between the account
private key and the validation query made by the server, since the fingerprint of the account key is contained in the service
code token used for authorization. The entity code token is initially obtained through a secure exchange between the entity requesting certificates and the
administrative authority
that is responsible for determining what entities can request certificates.
&rfc2119;
&rfc7515;
&rfc7518;
&rfc7519;
&rfc7638;
&I-D.ietf-acme-acme;
NIST FIPS 180-4,
Secure Hash Standard Department of Commerce, National
&rfc7340;
&I-D.ietf-stir-rfc4474bis;
&I-D.ietf-stir-certificates;
&I-D.ietf-stir-passport;
&I-D.ietf-acme-telephone;
&I-D.ietf-acme-service-provider;